What should be considered when selecting a gearbox?

Operating conditions of the gearbox (engine type, type of application, daily operating time, number of start-ups, nature of the load etc.) and environmental conditions should be taken into consideration. The service factor should be taken according to these conditions.

What is service factor?

Service factor is a multiplier applied to the power or torque needed for an application. The resulting power or torque should be less than the nominal power (also called the mechanical rating) or torque of the selected gearbox. This is necessary so that the gearbox can operate at a certain safety under certain operating conditions.

How is the service factor of the gearbox determined?

The service factor is determined according to characteristics of the application.

These include engine type, daily operating time, starting frequency, nature of the load etc.

How is the service factor calculated?

It is the ratio of the nominal power of the gearbox at a given output speed to the motor power used. It is also the ratio of the nominal torque of the gearbox to the operating torque.

What is the nominal torque rating of the gearbox?

It is the torque value that the gearbox can transmit continously.

What is the maximum torque rating of the gearbox?

It is the torque value that the gearbox can transmit momentarily.

What is thermal power?

The maximum power that a gearbox can transmit without overheating under certain ambient conditions.

Thermal power of gearbox depends on the size of external surface of the gearbox housing, ambient temperature, operation area (covered place or open air) and the operation time in an hour.

If the gearbox is cooled with air or the gearbox oil is cooled, thermal power can be increased by 10% – 100% depending on the effect of the cooling.

Under which circumstances a cooling system should be used in a gearbox?

Depending on the environmental conditions, generally, the cooling system should be used when the thermal power of the gearbox is lower than the engine power to be used.


What kind of oil is used in gearboxes?

Mineral gear oils or synthetic gear oils are used depending on the environmental conditions and the gearbox type. The lubricant must contain additives that provide corrosion protection, oxidation resistance and wear prevention.

PAO-based synthetic gear oils have a wider operating temperature range and higher viscosity index values than mineral oils.

What is the maximum allowed operating temperature for gearboxes?

The gear oil used in the gearbox is the determining factor. PAO-based synthetic gear oils have a wider operating temperature range than mineral oils.

Operating temperature range of mineral oils: -20°C and +60°C (burst: +80°C)

Operating temperature range of PAO-based synthetic oils: -45°C and +80°C (burst: +100°C)

What are the recommended oil change intervals for gearboxes?

Oil change is recommended every 5,000 hours of operation for mineral oils, and every 15,000 hours of opearation for synthetic oils.

These values assume an average oil temperature of 70°C. Actual oil lives may be shorter or longer. As a general rule, oil life decreases by half for every additional 10°C of operating temperature above 70°C.

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